The Effect of Netting Dissipaters on Increasing the Efficiency of Energy Dissipation in Vertical Drops

Abrupt changes of the channel bed elevation in hydraulic systems, e.g. in chutes, drops and steeped spillways, results to create a sever flow kinematic energy. This excess energy, can tend to different phenomena, such as tremendous forces, scouring and degrading the channel bed, resulting to destruction of the downstream hydraulic structures. The most important source to cause this phenomena is the the existence of sequent vertical drops along the the channel. In this study, the energy dissipation efficiency was increased by installing a new type of dissipaters namely netting dissipater on the crest of the vertical drops based on model experimtation. Also, the features of hydraulic jump, created in the stilling basin, were compared to those of a simple vertical drop. By assembling the above mentioned structure to the top of the stilling basin, the jet flow direction is changed, the degree of turbulence is increased and as the results, the kinematic energy loss increases and the length of the hydraulic jump decreses. The enhanced efficiency of the proposed structure was quantified based on the achieved experimental data.

Isotope hydrograph separations and rapid delivery of pre-event water from drainage basins

Environmental isotopes, such as oxygen-18 and deuterium, have been used increasingly to separate stormflow into its event and pre-event components in order to elucidate the sources, pathways and residence times of water in drainage basins. The majority of isotopic hydrograph separations indicate that pre-event water supplies at least 50% of streamflow at peak discharge in small- and medium-sized basins; however, there is no consensus as to the means by which pre-event water is rapidly exported from drainage basins. The hydrological processes that have been invoked to explain the observed isotopic response of streamflow to rainfall and snowmelt inputs in various environments are reviewed. These processes include groundwater ridging, translatory flow, macropore flow, saturation overland flow, kinematic waves and release of water from surface storage. Tests of the ability of the hypothesized mechanisms to explain the isotopic signature of stormflow from drainage basins will require a more complete integration of hydrometric methods with the use of environmental isotopes than has been achieved previously. Along with various methodological issues associated with the isotopic hydrograph separation technique, the overall relevance of these hydrograph separations to the understanding and prediction of stream hydrochemistry must be evaluated critically.